Drive circuit for providing at least one of the output waveforms having at least four different voltage levels

Abstract

A drive circuit comprises a first waveform generator and a second waveform generator. Each waveform generator is capable of generating at least two voltage states and the instantaneous voltage of the first waveform is never less than that of the second waveform by more than a defined amount. The circuit further comprises a plurality of means to produce respectively a plurality of output waveforms by selectively switching to either the first waveform or the second waveform and a gate array to control the selective switching. The arrangement is such that each of the plurality of means to produce respectively a plurality of output waveforms is capable of producing an output waveform having at least four voltage states. The drive circuit produces a plurality of outputs suitable for driving a matrix-addressed display.

I claim: 
     
       1. A drive circuit for producing a plurality of output waveforms for driving a matrix addressed display, the drive circuit comprising; a first signal generating circuit for providing a first waveform having at least two voltage levels, a second signal generating circuit for providing a second waveform having at least two voltage levels; a display driver arranged to receive the first and second waveforms and having a plurality of output terminals, each terminal arranged for outputting at least one of the first and second waveforms to the display; a control circuit for controlling the output of the display driver, thereby to effect a plurality of output waveforms from the display driver for driving the display such that at least one of the output waveforms has at least four different voltage levels. 
     
     
       2. A drive circuit according to claim 1 wherein the first and second waveforms each have three voltage levels and the first and second waveforms are arranged such that the instantaneous voltage of the first waveform is never less than the instantaneous voltage of the second waveform by more than a predefined amount whereby the driver circuit is caused to provide at least one output waveform having at least five different voltage levels. 
     
     
       3. A drive circuit according to claim 2 wherein at least one of the first and second waveforms includes a relatively high frequency component to comprise two of said at least two voltage levels of the at least one of the first and second waveforms. 
     
     
       4. A drive circuit according to claim 1 wherein at least one of the first and second waveforms includes a relatively high frequency component to comprise two of said at least two voltage levels of the at least one of the first and second waveforms. 
     
     
       5. A drive circuit according to claim 1 wherein the first and second signal generating circuits comprise first and second multiplexer circuits each having a plurality of inputs, the first and second multiplexer circuits each being arranged to receive a respective one of a plurality of voltage levels on each input, and wherein the control circuit is arranged to provide further control signals to the first and second multiplexer circuits, the first and second multiplexer circuits being arranged to provide, respectively, the first and second waveforms each having the at least two voltage levels from the plurality of voltage levels on the plurality of inputs in response to the further control signals received thereby. 
     
     
       6. A drive circuit according to claim 1 comprising a plurality of opto isolator circuits between the control circuit and the driver circuit for affording the control signals to the driver circuit. 
     
     
       7. A drive circuit according to claim 1 wherein the driver circuit comprises a plurality of shift register circuits and a respective plurality of latch circuits. 
     
     
       8. A drive circuit according to claim 1 wherein the control signals comprise binary coded control signals. 
     
     
       9. A display device comprising a matrix-array type liquid crystal cell including a liquid crystal layer, a first set of electrodes and a second set of electrodes, said first and second set of electrodes overlapping to provide areas of overlap for defining a plurality of pixels in the liquid crystal layer, the display device further comprising a first drive circuit for producing an output waveform for each of said first set of electrodes and a second drive circuit for producing an output waveform for each of said second set of electrodes wherein at least one of said first drive circuit and said second drive circuit comprises a first signal generating circuit for providing a first waveform having at least two voltage levels, a second signal generating circuit for providing a second waveform having at least two voltage levels, a display driver circuit arranged to receive the first and second waveforms, and having a plurality of output terminals adapted to receive either the first or second waveforms, and a control circuit for providing control signals for controlling the output of the driver circuit whereby the display driver circuit, in response to the control signals, provides to the electrodes coupled thereto, a plurality of waveforms for driving pixels of the display, at least one of the waveforms for driving pixels of the display having at least four different voltage levels. 
     
     
       10. A method of producing a plurality of output waveforms for driving a matrix addressed display, the method comprising generating simultaneously a first and second waveform, each one of said first and second waveforms having at least two voltage levels, affording the first waveform to a first voltage supply terminal of a display driver circuit, affording the second waveform to a second voltage supply terminal of the display driver circuit, whereby the first and second waveforms are caused to act, respectively, as first and second supply waveforms for the display driver circuit, generating a plurality of control signals, affording the control signals to control input terminals of the display driver circuit for controlling switching of the first and second voltage supply terminals of the display driver circuit to output terminals of the display driver circuit, thereby to enable the display driver circuit to provide a plurality of output waveforms for driving the display, in response to the control signals, at least one of the output waveforms having at least four different voltage levels.